Perovskite-carbon composites synthesized through in situ autocombustion for the oxygen reduction reaction: the carbon effect

- Carbon in nanocomposites reduces the particle size of perovskite and decrease the agglomeration degree in composite, allowing a better dispersion and an increase of the number of active sites.
- Strong interaction of the perovskite oxide with carbon is evidenced by the carbon-fraction dependent mean oxidation state of Mn.
- The ORR activity measured for the ISAC nanocomposites increases with the fraction of carbon in nanocomposites.
- The ORR activity is also influenced by the mean oxidation state of Mn of the perovskite in the composites.

In this study, the authors synthesized perovskite-carbon composites by the In Situ AutoCombustion (ISAC) method. By physical-chemical characterization it was observed that nanoparticles of the LaMnO3±δ perovskite phase are well dispersed in the carbon matrix and are primarily located in the mesopores and small macropores of the Vulcan carbon. By electrochemical methods it was concluded that the oxygen reduction reaction (ORR) activity improvement of ISAC composites relative to perovskite/carbon composites prepared by mixing is due to the ISAC synthesis route and to the presence of carbon in the composites, which act by reducing the particle size of the perovskite, and decreasing their agglomeration degree. These result in the higher dispersion of perovskite particles and the ensuing increase of the number of catalytically active sites. Results of temperature programmed reduction reaction, X-ray photoelectron and electron energy loss spectroscopies suggest that perovskite particles in ISAC composites have lower oxygen stoichiometry compared to the unsupported LaMnO3 and are reduced by H2 at lower temperatures.

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